1. Field of the Invention
This invention relates to radio signal receivers. More particularly, this invention relates to improvements in the noise reduction circuitry of a radio receiver.
2. 2. Description of the Related Art
FIG. 4 illustrates the conventional radio receiver. A front end preselect filter 10 accepts a radio frequency signal and passes a preselected band of radio frequency signals to the mixer 12. The mixer 12 mixes the RF signal from the filter 10 with an intermediate frequency supplied by the variable oscillator 14. The intermediate frequency (IF) signal passes through the crystal filter 16 which selects a band of IF frequencies to pass to the IF amplifier 18. The selectivity of the receiver is dependent on the bandpass of the crystal filter 16. After amplification in the IF amplifier 18, the IF signal is translated into an audio frequency by the product detector 20, which mixes the IF signal with a beat frequency signal supplied by the beat frequency oscillator 22. The audio signal from the product detector 20 is amplified by the audio frequency amplifier 24 and input to a speaker 26.
The signal travelling through the circuit of FIG. 4 includes several known forms of noise. Specifically, but not exclusively, the RF signal input to the filter 10 may be subject to atmospheric noise and the signals passing through the electronic elements 10 through 26 may be subject to receiver generated electronic noise. As is well known in the art, the extent of noise in the signal received and processed by the receiver limits the ability of the receiver to detect particular RF signals.